The goals of this project are: (1) to develop more sensitive in vivo measures of the presence and progression of HIV effect on brain function and pathology, and (2) using these measures, to elucidate and quantitate the temporal and spatial patterning of the progression of brain involvement in HIV disease. Such objective measures of effects of HIV on the brain are essential for monitoring the effects of therapeutic interventions on disease pathology and function impairment. Our ongoing studies have documented both structural and functional deficits in cognitively impaired seropositive (CISP) patients, and functional deficits in cognitively impaired seropositive (CNSP) patients. The functional deficits involved increased latency of the frontal P3A component of the brain electrical evoked potential (EP). The structural deficits involved demonstration and replication of antemortem reductions in N-acetylaspartate (NAA) concentrations throughout a supraventricular brain volume using 1H MRSI. This application extends these initial observations, testing the following hypotheses: 1: (a) In cognitively impaired HIV+(CISP) patients compared to HIV-high risk controls, NAA reductions will be largest in the subcortical gray matter, and (b) within the CISP patient group, average NAA concentrations in the subcortical gray matter will be proportional to the severity of neuropsychological impairment and/or the degree of P3A latency prolongation 2: (a) Cognitively normal HIV+(CNSP) patients with relatively long- standing HIV infection, compared to high-risk controls, will demonstrate reductions in subcortical gray matter and (to a lesser extent) deep white matter NAA, and increases in P3A latency; (b) the magnitude of the subcortical gray matter and deep white matter NAA reductions observed will be proportional to the increase in P3A latency. 3. Changes in neuropsychological function over time with HIV disease progression will be associated with decreases in NAA and increases in P3A latency. Positive responses to treatment will be associated with either an arresting of the progression of NAA and P3A changes or with recovery of NAA and P3A deficits. These specific aims will be accomplished using longitudinal 1H MRSI and EP investigation of 30 CISP and 40 CNSP patients compared to both high- risk and low-risk controls. CISP and CNSP subjects will be studied with replacement of subjects who either die or drop out of the study so that the replicability of results regarding the spatial and temporal patterning of disease progression can be established.